Mari Gilbert, the mother of Shannan Gilbert — whose remains were discovered near Gilgo Beach five years ago — was found dead Saturday in the upstate Ellenville apartment of another daughter, who has been charged with the killing, police said Sunday.

Sarra Elizabeth Gilbert, 27, was charged with second-degree murder and fourth-degree criminal possession of a weapon, Ellenville police said in a news release posted on Facebook.

Police said Mari Gilbert, 52, was killed Saturday morning at 9 Warren St. in apartment No. 2, which records show as Sarra Gilbert’s residence. Her body was found at 2:15 p.m.

“Shortly thereafter, Ellenville police located and took into custody her daughter,” the release said.

Sarra Gilbert was arraigned and remanded to the Ulster County Jail without bail, police said.

Gilbert family attorney Johnny Ray, citing conversations with police and family members, said at a news conference in his Miller Place offices that Sarra Gilbert “invited” her mother over to talk and then stabbed her in the living room.

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Mari Gilbert’s longtime partner, Elroy Shulterbrandt, discovered the killing “as he went through one of the windows trying to locate her,” Ray said.

Ray, who represented the Gilbert family in lawsuits related to Shannan Gilbert’s death, said Sarra Gilbert had been “hearing voices for several days” before the stabbing. Ray said he isn’t representing Sarra Gilbert in the homicide case, but thinks she was “not competent” and “not in control of her own faculties.”

Shulterbrandt, speaking at Mari Gilbert’s Ellenville home less than a mile from her daughter’s apartment, called Mari Gilbert a “wonderful” woman, but said he was too emotional to say more.

“The more I talk about it, the more I break down,” he said. “So the less I can talk about it, the more I can keep myself up.”

Shannan Gilbert, 24, a sex worker, disappeared in May 2010, near a remote stretch of Ocean Parkway. The search for Gilbert uncovered 10 sets of human remains that police said may have been the work of one or possibly more serial killers. Shannan Gilbert’s body was found in nearby Oak Beach on Dec. 13, 2011.

Mari Gilbert had been a vocal advocate for her daughter after Shannan’s death, pressing police on the investigation and filing a wrongful-death suit against Peter Hackett, the last person known to have seen Gilbert alive before she apparently ran into a nearby marsh from his home. A Suffolk County judge later dismissed much of that suit.

On the night she disappeared, Shannan Gilbert, of Jersey City, made a frantic early morning 911 call from the home of a client, Joseph Brewer, then pounded on Hackett’s door, police have said. Neither man has been charged in the case.

Shannan Gilbert, 24, of Jersey City, center, disappeared in May 2010, near a remote stretch of Ocean Parkway. The search for her remains uncovered other human remains in the surrounding areas. Gilbert's remains were found in Oak Beach on Dec. 13, 2011. Photo Credit: Handout

A K-9 officer conducting a routine exercise and searching for Gilbert stumbled on a body that eventually led to the discovery of a dumping ground of remains along Ocean Parkway.

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Since then, Gilbert’s death and the mystery of who killed the 10 others have confounded investigators. They have said Gilbert’s death is not linked to the other victims.

At a 2015 news conference, Mari Gilbert said she was not satisfied with the way police handled the investigation.

“I was very angry, as any parent should be, but as time went by I kind of realized that maybe that was her destiny to help other families,” Mari Gilbert said at the time.

A December 2011 autopsy on Shannan Gilbert’s remains by the Suffolk County medical examiner failed to determine the cause or manner of her death.

Mari Gilbert’s sister, Lori Grove, 56, of Williamsburg, Pennsylvania, was waiting Sunday morning to hear from her niece Sherre Gilbert, Sarra Gilbert’s sister, about what happened.

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“All I know is she’s gone,” Grove said of her sister. “Mari lived a very tumultuous life, a hard life — not always by her own decisions.”

Grove said she spoke to Mari Gilbert, the youngest of five children, a few days ago about “her desire to leave a positive Christian legacy to her family.”

Jim O’Rourke, the Port Jefferson-based attorney for Hackett, said it was unclear whether a motion to dismiss the Gilberts’ case against him, scheduled to be heard Tuesday, would go forward. He said the suit wouldn’t automatically be dismissed and Mari Gilbert’s other daughter could be named as a successor representative. Ray said Sherre Gilbert has volunteered to take that role.

Ellenville police have scheduled a news conference about the arrest for Monday.